Articles

Taking Off With Pterosaurs

Taking off with pterosaurs, as described in articles in BBC News and PLoS ONE 15 November 2010 and ScienceDaily 24 November 2010. Pterosaurs are extinct winged reptiles, some of which were so large that scientists have wondered how they could take off and fly because estimates of the body mass of some of them are well above the maximum size of flying birds. However, as Mark Witton of Portsmouth University, UK, says: “These creatures were not birds; they were flying reptiles with a distinctly different skeletal structure, wing proportions and muscle mass.”

Witton and a colleague, Michael Habib of Chatham University, Pennsylvania have examined pterosaur bones, estimated their size and weight, and calculated bone strength and flight mechanics. They estimated the largest of them may have weighed between 200 and 250 kg, with a wingspan of 10 – 11 metres.

One intriguing finding was the relative robustness of the wing bones, especially the humerus (upper arm bone) compared with birds. Witton explained: “Pterosaurs had incredibly strong skeletons: for their weight, they're probably amongst the strongest ever evolved. And unlike birds, where the wings become relatively weak as they grow in size, those of pterosaurs do the opposite: they become stronger. As pterosaurs became larger, they reinforced their wings and expanded their flight muscles to ensure they could keep flying.”

Based on their findings Witton and Habib suggest pterosaurs used their wings to help them take off, using a pole vault action to propel themselves off the ground. Habib explained: “Instead of taking off with their legs alone, like birds, pterosaurs probably took off using all four of their limbs. By using their arms as the main engines for launching instead of their legs, they use the flight muscles, the strongest in their bodies, to take off and that gives them potential to launch much greater weight into the air. When they were far enough off the ground, they could start flapping their wings before finding a thermal or another area of uplift to gain some altitude and glide off to wherever they wanted to go.”

Once in the air they are faced with the problem of staying aloft and then landing. Colin Palmer, an engineer has carried out an aerodynamic study using models of pterosaur wings in a wind tunnel. His results indicate pterosaurs “were adapted to fly in a slow, controlled manner in gentle tropical breezes” using the lift from rising air currents. Their wings were also suitable for landing slowly. Although their bones were larger and more robust than birds, they were still relatively fragile, and the creatures could not risk any crash landings. Palmer explained: "Since the bones of pterosaurs were thin-walled and thus highly susceptible to impact damage, the low-speed landing capability would have made an important contribution to avoiding injury and so helped to enable pterosaurs to attain much larger sizes than extant birds. The trade-off would have been an extreme vulnerability to strong winds and turbulence, both in flight and on the ground, like that experienced by modern-day paragliders.”

Editorial Comment: Mark Witton is right - pterosaurs were not birds and should not be compared with them. They were unique creatures that show no signs of having evolved from, or into, any other creature. The pole vault theory of pterosaur take offs sounds reasonable, but that only affirms they had a unique design that could not function until the creatures had all the other features needed for flight. The study by Colin Palmer provides some insight into how they functioned and why they died out. In the original good world that God made the atmosphere would have been thicker, with more water and carbon dioxide and oxygen, and therefore would have supported these enormous creatures. This good world would not have had highly turbulent winds either, as summer and winter were absent until Noah’s Flood so therefore pterosaurs could land safely. After Noah’s flood the climate degenerated rapidly to the weather patterns we have today, with extremes of temperature and strong turbulent winds. Sadly this meant these extraordinary creatures could not survive, and their fossils remind us how far downhill the world has devolved. (Ref. biomechanics, palaeontology, extinction, aerodynamics)